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Background Human milk is the ideal source of nutrition for infants, especially during the first six months of life. Milk components can protect against inflammation and infection, and stimulate immune maturation. In cases where mothers are unable to express breastmilk, pasteurised donor milk is a preferred option. Distributed from human milk banks, donor milk is particularly important to preterm infants. Born with an immature gut, these infants are at risk of developing diseases such as necrotising enterocolitis and sepsis. While Holder pasteurisation of breastmilk is recommended, this and other heat treatment processes can lead to the inactivation of bioactive components and change the composition and content of the major milk components. Scope and approach This review examines previous studies on the impact of pasteurisation of human milk on the bioactivity of proteins, content and composition of oligosaccharides and lipids. More recent studies investigated the effect of pasteurisation on the enzymatic properties of bile salt-stimulated lipase, which naturally occurs in human milk and contributes to lipid digestion and absorption. These studies highlight the potential consequence of pasteurised donor milk on the growth and development of an infant. Key findings and conclusion The bioactivity of proteins is reduced due to pasteurisation thereby hindering their ability to exert their immunological properties. However, the content and composition of oligosaccharides and lipids still remain the same following heat treatments. Despite this, the decrease in activity of lipases would impair the digestion and absorption of lipids. It is thus critical to ensure that conditions such as the temperature and heating time are chosen carefully when pasteurising donor human milk.

Human milk is critical for the survival and development of infants. This source of nutrition contains components that protect against infections while stimulating immune maturation. In cases where the mother's own milk is unavailable, pasteurized donor milk is the preferred option. Although pasteurization has been shown to have minimal impact on the lipid and FA composition before digestion, no correlation has been made between the impact of pasteurization on the FFA composition and the self-assembly of lipids during digestion, which could act as delivery mechanisms for poorly watersoluble components. Pooled nonpasteurized and pasteurized human milk from a single donor was used in this study. The evolving FFA composition during digestion was determined using GC coupled to a flame ionization detector. In vitro digestion coupled to small-angle X-ray scattering was utilized to investigate the influence of different calcium levels, fat content, and the presence of bile salts on the extent of digestion and structural behavior of human milk lipids. Almost complete digestion was achieved when bile salts were added to the systems containing high calcium to milk fat ratio, with similar structural behavior of lipids during digestion of both types of human milk being apparent. In contrast, differences in the colloidal structures were formed during digestion in the absence of bile salt because of a greater amount of FFAs being released from the nonpasteurized than pasteurized milks. This difference in FFAs released from both types of human milk could result in varying nutritional implications for infants.

Hypothesis The digestion of different milks and milk substitutes leads to the formation of a variety of self-assembled lipid structures, with the structuring of human milk being paramount for infant nutrition. It was hypothesised that mixing cow milk fat rich in medium/long-chain lipids with canola oil rich in long-chain unsaturated lipids would replicate the structuring of human milk by balancing lipid chain lengths and saturation levels. Experiments Emulsions of cow milk fat/canola oil mixtures were prepared in two ways – by pre-mixing ghee and canola oil before dispersing them and by dispersing canola oil directly into commercial cow milk. Small angle X-ray scattering combined with titration of the fatty acids produced during digestion allowed for the correlation of dynamic lipid self-assembly with the extent of lipid digestion. Laser light scattering was used to show that the particle sizes in the digesting mixtures were similar and coherent anti-Stokes Raman spectroscopy (CARS) microscopy was used to confirm the mixing of canola oil into cow milk fat globules. Findings As the amount of long-chain unsaturated canola oil lipids in the mixtures increased, the lipid self-assembly tended towards colloidal structures of greater interfacial curvature. When the ratio of cow milk fat to canola oil lipids was 1:1 (w/w), the digesting lipids assembled themselves into the same liquid crystalline structures as human breast milk. This observation was independent of the method used to mix the lipids, with CARS microscopy indicating uniform mixing of the canola oil into cow milk upon ultrasonication.

Oral delivery of dispersible tablets is a preferred route of administration for paediatrics due to ease of administration and dose control. Milk has gained interest as a drug delivery system due to its ability to dissolve poorly water-soluble drugs. There are no reports of milk tablet formulations being assessed in the context of lipid digestion, which is critical in influencing orally administered drug solubility and bioavailability. Milk-drug tablets were formulated by blending freeze-dried bovine milk or infant formula with the poorly water-soluble drug cinnarizine, which were directly compressed. Tablet strength, friability and dispersibility were quantified and synchrotron X-ray scattering was used to determine the lipid liquid crystalline phases formed during in vitro digestion of dispersed tablets and their effects on drug solubilisation. Tableting had a significant impact on the self-assembly of lipids in redispersed milk tablets whereas no effect was seen for infant formula tablets. Incorporation of the disintegrant poly(vinylpolypyrrolidone) to reduce tablet dispersion times promoted the formation of hexagonal liquid crystalline phases upon digestion but had minimal effect on drug solubilisation. These findings show that similar to the use of liquid milk, the formulation of milk-drug tablets can be used to improve solubilisation of poorly water-soluble drugs.